Curtain Walling Calculator

Curtain walling is a non-structural external cladding system, typically aluminium-framed with glazed or opaque infill panels. It hangs from the building's structural frame like a curtain and must resist wind loads, thermal movement and water penetration while meeting Part L thermal and Part B fire requirements.

In 2026, stick-system curtain walling with double-glazed units typically costs £400-£600/m² supply and install. Unitised systems range from £600-£900/m². Point-fixed structural glass is the most expensive at £700-£1,100/m². Costs vary with height, access, specification and finish.

Under Approved Document L Volume 2 (Buildings other than dwellings), 2021 edition, Table 4.1 sets the limiting (maximum) U-value for "all other windows, roof windows, curtain walling" at 1.6 W/m²K. This is the worst value an individual element may have. Overall compliance is assessed against the notional building defined by the National Calculation Methodology (SBEM/DSM), which varies by building activity and glazing area rather than a single published figure. Enhanced thermal breaks and triple glazing can achieve below 1.0 W/m²K.

Stick systems are assembled on site piece by piece from mullions, transoms and glazing panels. Unitised systems arrive as pre-assembled factory-made modules that are craned into place. Unitised is faster on site but more expensive, making it suited to large-scale commercial projects.

A typical double-glazed curtain walling system weighs approximately 35-45 kg/m², while triple-glazed systems weigh 50-60 kg/m². The structural engineer must account for this dead load plus wind loading when designing the primary structure and fixing brackets.